1. Field of the Invention
The subject matter of the present invention relates generally to an input apparatus for a multi-channel device, such as a logic analyzer, which provides said multi-channel device with a programmable set-up and hold feature wherein the set-up and hold times of a data signal acquired by said input apparatus, relative to a clock signal, are programmable by a user.
2. Description of the Prior Art
Most advanced electronic equipment in use today include complex integrated circuit logic systems, such as those used in microprocessors. Complicated multi-channel devices, such as a logic analyzer, are used for trouble-shooting these logic systems. The multi-channel device includes a multi-channel probe attached thereto, for example, a 4 channel probe for acquiring a plurality of logic signals from the logic system. The logic signals are stored in an acquisition memory within said multi-channel device. The stored logic signals are retrieved therefrom for display on the multi-channel device. A large number of cables are used for connecting each probe to the multi-channel device. Usually, the length of any one cable is different than the length of any of the other adjacent cables. The logic signals must be transmitted through these cables prior to storage in the acquisition memory. However, if a particular cable is longer than another adjacent cable, a longer period of time is required for the logic signal to be transmitted through the former cable than it is for the logic signal to be transmitted through the adjacent cable. Any difference in cable length, among these cables, results in skewed logic data signals displayed on the cathode ray tube (CRT) screen of the multi-channel device. These skewed data signals introduce a measurement error. Skewed logic data signals are also produced as a result of differences in propagation time delay through the input circuitry of the logic analyzer. This measurement error is not acceptable, especially when it occurs in conjunction with high-frequency, or high-acquisition rate test instruments. In order to eliminate this measurement error, the multi-channel device includes an input apparatus which compensates for the differences in cable length existing within the channels of said multi-channel device. The input apparatus therefore, ensures that the acquired data is displayed properly on the CRT screen, and thereby eliminates the possibility of introducing the above measurement error. However, in order to properly store the logic signals in the acquisition memory, the set-up and hold times of the logic signal generated by the logic systems being tested, and acquired by the multi-channel device, relative to an external clock signal, must be set to predetermined values.
Further, the set-up and hold times of the acquired logic signal generated by the logic system being tested, relative to the external clock signal, are usually different than the predetermined values. Therefore, the acquired logic signal cannot be properly stored in the acquisition memory. Consequently, the multi-channel device cannot be used to troubleshoot these logic systems. This severely limits the usefulness of the multi-channel device.